All that aside, the choice of B412 in a training role - particularly for students straight off initial helicopter course - does seem a little odd to me.
I think it was a question of what was available at the time - the aircraft needed to be a twin, with a big enough cabin for rearcrew training, the capability for winching, underslung loads, SAR etc and be robust enough for intensive military flying training - the 412 seemed to do a pretty good job for nigh on 20 years.
The DHFS single squirrel to 412 training regime replaced the RAFs Gazelle to Wessex training pipeline (which again had worked very well for many years) the new variant, MFTS with 135 all through and a smattering of 145 at the end, doesn't seem to be faring quite so well.